First of all, don't sweat brush-painting.. With practice, brushed finishes can rival airbrushing on some subjects, especially those that get heavily weathered, like AFVs..
Second, don't worry about buying an airbrush right away either, until you've got some "rattle-can time".. Airbrushing is an art that takes a long time to master, paint-mixing takes a while to learn to do right, and it's a high-maintenence (and expensive) tool... If you're just wanting an evenly-applied one or two-color finish, rattle-cans are your best bet to flatten the learning curve..
The cheaper airbrushes, like the Testor's Airbrush are pretty good for your first attempts, and although they have nowhere near the fine-line control that top-end airbrushes do, they go a long way in helping you to learn surface-prep, learn to mix paint to the proper viscosity, learn how to mix colors, learn the different applications and thinners for acrylics vs enamels, allow using rattle-cans AND bottle paints together, and also allow you to start experimenting with airbrush-effects like fading paint and "dusting"...
Folks who run out and but high-end airbrushes and compressors and a book on "How to Airbrush" and attempt to airbrush a free-hand mottled camouflage on a Ju-88 nightfighter will likely ruin it or ruin their first paint-jobs with it..
A word about "store-bought" weathering products too..
Weathering is a process that's made up of several steps, each involving a different technique and different material.. A good weathering job involves the use of washes, drybrushing, and pastels or powders... Techniques used for armor models are oftentimes too heavy-handed for use on aircraft... Then there's the things that you have to analyze as you look at it..
That crystal-clear canopy is gonna look wrong on a dirty, beat-up, and sun-faded P-39 based in North Africa, but that dirty winshield is gonna look silly on a high-gloss candy-apple red Dodge Charger... That paint-chipping on the leading edges of that F-16 operating from Luke Air Force Base is gonna look outta place too.. Not to mention that you shouldn't have applied all that silver paint to the leading edges of the B-17 you built, since those black edges on the wings are rubber de-icing boots..
So there're no "one-bottle" solutions to weathering.. It takes a while to learn, and it takes a while longer to know what goes on what..
But meanwhile, enjoy the ride!
Welcome to the forums..